ENHANCED HOT-CARRIER-DEGRADATION IN LDD MOSFETS UNDER PULSED STRESS

Hot-carrier degradation of lightly doped drain (LDD) MOSFET's under ac stress is investigated. Enhanced ac degradation occurs in LDD MOSFET's as well as in single drain MOSFET's. However, there is a peculiar degradation mechanism in LDD MOSFET's. For single-drain MOSFET's, enhanced ac degradation appears in both threshold voltage and transconductance at stress drain voltages larger than a critical value. On the other hand, for LDD MOSFET's, although the enhanced degradation in threshold voltage and transconductance appears at stress drain voltages larger than a critical value, the enhanced degradation in transconductance appears even under stress drain voltages lower than the critical value. The difference in the ac-enhanced degradation between LDD and single-drain structures can be explained by a hot hole generated neutral-electron-trap model and the change in hot-hole-injected oxide region according to stress bias conditions.